This application claims priority from German application FRG 201 02 076.9, filed Feb. 7, 2001, and the contents of this German application are incorporated herein by reference in their entirety.
The present invention relates to a device for braking a motor shaft, especially for a motor shaft in a chain saw, with a brake band that at least partially surrounds an area of the shaft.
In implements comprising rotating masses a rapid braking of these masses is often desired. For example, a drum brake consisting of brake band and coupling (or clutch) drum are used to brake a chain in a chain saw. The brake bands are asymmetrically designed in this instance for an optimum utilization of material, relative to the forces occurring during braking. Furthermore, the deep-drawn coupling drums have a conicity of their outer circumference, which results in an axial force, in the interplay with the asymmetry of the braking and during the braking process, that can allow the brake band to slip off the coupling drum.
In order to secure the brake band from slipping off axially during the engagement of the brake, e.g., the area around the coupling drum is very tightly closed by an additional housing covering so that the brake band is axially secured in the braking state. A very precise positioning of the parts to each other is necessary in order to assure such a securing. In addition, a brake band heated by the braking process can damage or melt plastic coverings upon making contact with them.
In other known solutions tongues (or flaps) are welded onto the brake band that are guided in radial offsets (relative to the axis of rotation of the coupling shaft) of the component guiding the brake band, e.g., a crankcase. This means additional components, sources of errors in the production and therefore increased production costs.
The invention therefore addresses the basic problem of providing a device for braking a motor shaft with a brake band which device makes possible an exact guidance of the brake band without additional, separate components on the brake band and the surrounding housing.
The invention solves this problem in that the brake band comprises at least one projection designed in one piece with the brake band. It is possible, due to the features of the invention, that an exact guidance of the brake band is assured without additional components on the brake band or the housing, which eliminates additional costs for components that hold the brake band in position.